The present invention relates generally to cartography. In particular, the present invention relates to computerized techniques for extracting height information for an arbitrary-image point on an image that is mapped to a coordinate system and to generating a representation of the image that includes the height information. More particularly, embodiments of the present invention relate to computerized techniques for extracting height information for arbitrary-image points on a map given a two or more aerial images having respective sets of rational polynomial coefficients, and to generating a topographic image map that includes the extracted height information.
To locate a street, navigate a mountain trail, or target a laser guided missile, maps provide valuable information for the success of each. Relatively simple maps, such as road maps, typically provide two-dimensional (2D) flat information and forgo the inclusion of topographic information. For the automobile driver, 2D flat information, such as longitude and latitude, is often sufficient as the driver may not be terribly concerned if her path leads her up hill or down into valleys. Mountaineers, on the other hand, who propel themselves under their own power have a keen interest in knowing whether their path will traverse a landscape of steep hills and/or deep valleys. Having such interest, the mountaineer is likely to make use of a contour map having topographic information to ascertain the escarpment of their trek. Others interested in maps that include height information include fighter pilots who may require the height information for targeting and firing a missile.
Generating maps having height information often involves extraction of height information from a set of stereo photographs. The extraction of height information from stereo photographs is typically a labor intensive and costly process. For example, the extraction of height information from a pair of stereo photographs typically involves a cartographer peering through a stereoscope for an extended period of time to extract height information for points in the stereo photographs. Modern technology has done relatively little to lower the cartographer's burden with respect to extracting height information from stereo photographs. For example, while stereo photographs slowly give way to stereo digital images, the extraction of height information from stereo digital images still includes the cartographer peering through a stereoscope for extended periods of time to extract height information for points in the digitized stereo images. Instead of placing a stereoscope on a set of stereo photographs, however, cartographers now place their stereoscopes over computer monitors on which digitized stereo images are displayed or use their computers as stereo workstations.
Not only is the extraction of height information from stereo photographs and stereo digital images relatively tedious, labor intensive, and costly, the generation of relatively high quality stereo photographs and stereo digital images is also relatively costly. For example, the generation of a set of stereo digital images often requires exclusive control of a satellite for a relatively lengthy period of time. To generate a relatively high quality pair of stereo images, exclusive control of a satellite may be required for five to ten minutes or more.
Accordingly, what is needed are time efficient and low cost methods for extracting height information from a set of photographs, and for generating topographic image maps that include the extracted height information.